Alcohol stays in your system for 24 hours or more?

Usually 12 hours... Usually, most alcohol that you consume (unless you drink enough to make yourself unconscious and sick enough to require hospitalization) is gone from your system in about 12 hours. If you have a bad enough hangover, those symptoms may stay around for 24 hours after you last drink... Just another reason to keep your alcohol consumption less than 2 drinks at a time.
Depends. On how your liver is working, what else is your liver having to do, and of course how much and how often you are drinking.